This invention is concerned with data handling and particularly directed to the data handling system used in the proposed Zenith/AT&T Digital Spectrum Compatible High Definition Television System (DSC-HDTV) which recently has undergone testing before the FCC. In that system, as disclosed and claimed in one or more of the above-identified copending applications, a digital high definition television signal is formatted into transmission frames, each comprising a pair of data fields which include a number of successive data segments. The initial segment of each field comprises a data field sync followed by 12 data segments of two level symbols, 240 data segments of either two level or four level symbols and 9 data segments of four level symbols. Each of the data segments is subdivided into a fixed number of subsegments. A transmission bit map, forming part of the first 12 data segments, identifies the two or four level character of the symbols in the 240 variable data segments. The subsegments are field interleaved by means of appropriate memories that are written to and read from in accordance with a predetermined algorithm. The data is line interleaved in a similar manner. A data correction system (Reed-Solomon) comprises the last 20 bytes of each four level data segment. The field and line interleaving are accomplished on a half field basis to conserve memory space. As disclosed in U.S. Pat. No. 5,086,340, the multilevel symbols of each field are preferably modulo N precoded to facilitate the use of a comb filter in the receiver for reducing NTSC co-channel interference.
As more completely disclosed in the copending application Ser. NO. 931,177, the subsegment symbol arrangement, and the line and field interleaving are selected to provide a high degree of rejection of NTSC co-channel signals, to guard against burst noise and to protect against vertically oriented interference from video edges in co-channel NTSC signals. The present invention is specifically directed to the technique for recovering (slicing) the incoming data, i.e. determining the level of the data, with particular regard to minimizing the amount of memory required for deinterleaving.